Detection Of Carbon Dioxide By Laser Resonance Absorption Spectroscopy

An analysis and description of a single laser resonance absorption spectrometer for the quantitative spectroscopic determination of carbon dioxide at 4.2 (mu)m is presented. The work consisted of the design and construction of a 4.2 (mu)m helium neon laser not available commercially, the construction of an optical spectrometer and signal processing unit and the determination of the carbon dioxide spectroscopic parameters required for calibration of the system.;The Fletcher Powell Method is used to locate the optimum laser frequency and broadening cross sections from absorption data for both pure carbon dioxide and nitrogen broadened carbon dioxide tests. Pure carbon dioxide absorption in a pressure range of 0.0016 atm (1.25 Torr) to 0.33 atm (250 Torr) is described well by a Lorentzian bandshape model with a self broadening cross section of 2.99 (+OR-) 0.30 GHz/atm at laser frequencies of 71.0730 (+OR-) 0.0008 THz (2370.74 (+OR-) 0.03 cm(\u27-1)) and 71.0847 (+OR-) 0.0008 THz (2371.13 (+OR-) 0.03 cm(\u27-1)). Nitrogen broadened carbon dioxide in the total pressure range of 0.13 atm (100 Torr) to 1.18 atm (900 Torr) is characterized by the same model with the laser frequency at 71.0835 (+OR-) 0.0012 THz (2371.09 (+OR-) 0.04 cm(\u27-1)) and the nitrogen broadening cross section of 2.40 (+OR-) 0.24 GHz/atm. The extinction coefficient for low concentrations of carbon dioxide in a 1 atm total pressure nitrogen environment has been determined as 9.90 (+OR-) 1.49 cm(\u27-1) atm(\u27-1)